145 research outputs found
The noise properties of 42 millisecond pulsars from the European Pulsar Timing Array and their impact on gravitational wave searches
The sensitivity of Pulsar Timing Arrays to gravitational waves depends on the
noise present in the individual pulsar timing data. Noise may be either
intrinsic or extrinsic to the pulsar. Intrinsic sources of noise will include
rotational instabilities, for example. Extrinsic sources of noise include
contributions from physical processes which are not sufficiently well modelled,
for example, dispersion and scattering effects, analysis errors and
instrumental instabilities. We present the results from a noise analysis for 42
millisecond pulsars (MSPs) observed with the European Pulsar Timing Array. For
characterising the low-frequency, stochastic and achromatic noise component, or
"timing noise", we employ two methods, based on Bayesian and frequentist
statistics. For 25 MSPs, we achieve statistically significant measurements of
their timing noise parameters and find that the two methods give consistent
results. For the remaining 17 MSPs, we place upper limits on the timing noise
amplitude at the 95% confidence level. We additionally place an upper limit on
the contribution to the pulsar noise budget from errors in the reference
terrestrial time standards (below 1%), and we find evidence for a noise
component which is present only in the data of one of the four used telescopes.
Finally, we estimate that the timing noise of individual pulsars reduces the
sensitivity of this data set to an isotropic, stochastic GW background by a
factor of >9.1 and by a factor of >2.3 for continuous GWs from resolvable,
inspiralling supermassive black-hole binaries with circular orbits.Comment: Accepted for publication by the Monthly Notices of the Royal
Astronomical Societ
A millisecond pulsar in an extremely wide binary system
International audienceWe report on 22 yrs of radio timing observations of the millisecond pulsar J1024â0719 by the telescopes participating in the European Pulsar Timing Array (EPTA). These observations reveal a significant second derivative of the pulsar spin frequency and confirm the discrepancy between the parallax and Shklovskii distances that has been reported earlier. We also present optical astrometry, photometry and spectroscopy of 2MASS J10243869â0719190. We find that it is a low-metallicity main-sequence star (K7V spectral type, [M/H] = â1.0, T eff = 4050 ± 50 K) and that its position, proper motion and distance are consistent with those of PSR J1024â0719. We conclude that PSR J1024â0719 and 2MASS J10243869â0719190 form a common proper motion pair and are gravitationally bound. The gravitational interaction between the main-sequence star and the pulsar accounts for the spin frequency derivatives , which in turn resolves the distance discrepancy. Our observations suggest that the pulsar and main-sequence star are in an extremely wide (P b > 200 yr) orbit. Combining the radial velocity of the companion and proper motion of the pulsar, we find that the binary system has a high spatial velocity of 384 ± 45 km s â1 with respect to the local standard of rest and has a Galactic orbit consistent with halo objects. Since the observed main-sequence companion star cannot have recycled the pulsar to millisecond spin periods, an exotic formation scenario is required. We demonstrate that this extremely wide-orbit binary could have evolved from a triple system that underwent an asymmetric supernova explosion, though find that significant fine-tuning during the explosion is required. Finally, we discuss the implications of the long period orbit on the timing stability of PSR J1024â0719 in light of its inclusion in pulsar timing arrays
Essential role of proteasomes in maintaining self-renewal in neural progenitor cells
Protein turnover and homeostasis are regulated by the proteasomal system, which is critical for cell function and viability. Pluripotency of stem cells also relies on normal proteasomal activity that mitigates senescent phenotypes induced by intensive cell replications, as previously demonstrated in human bone marrow stromal cells. In this study, we investigated the role of proteasomes in self-renewal of neural progenitor cells (NPCs). Through both in vivo and in vitro analyses, we found that the expression of proteasomes was progressively decreased during aging. Likewise, proliferation and self-renewal of NPCs were also impaired in aged mice, suggesting that the down-regulation of proteasomes might be responsible for this senescent phenotype. Lowering proteasomal activity by loss-of-function manipulations mimicked the senescence of NPCs both in vitro and in vivo; conversely, enhancing proteasomal activity restored and improved self-renewal in aged NPCs. These results collectively indicate that proteasomes work as a key regulator in promoting self-renewal of NPCs. This potentially provides a promising therapeutic target for age-dependent neurodegenerative diseases
High-precision timing of 42 millisecond pulsars with the European Pulsar Timing Array
International audienceWe report on timing, flux density, and polarimetric observations of the transient magnetar and 5.54 s radio pulsar XTE J1810-197 using the GBT, Nancay, and Parkes radio telescopes beginning in early 2006, until its sudden disappearance as a radio source in late 2008. Repeated observations through 2016 have not detected radio pulsations again. The torque on the neutron star, as inferred from its rotation frequency derivative f-dot, decreased in an unsteady manner by a factor of 3 in the first year of radio monitoring. In contrast, during its final year as a detectable radio source, the torque decreased steadily by only 9%. The period-averaged flux density, after decreasing by a factor of 20 during the first 10 months of radio monitoring, remained steady in the next 22 months, at an average of 0.7+/-0.3 mJy at 1.4 GHz, while still showing day-to-day fluctuations by factors of a few. There is evidence that during this last phase of radio activity the magnetar had a steep radio spectrum, in contrast to earlier behavior. There was no secular decrease that presaged its radio demise. During this time the pulse profile continued to display large variations, and polarimetry indicates that the magnetic geometry remained consistent with that of earlier times. We supplement these results with X-ray timing of the pulsar from its outburst in 2003 up to 2014. For the first 4 years, XTE J1810-197 experienced non-monotonic excursions in f-dot by at least a factor of 8. But since 2007, its f-dot has remained relatively stable near its minimum observed value. The only apparent event in the X-ray record that is possibly contemporaneous with the radio shut-down is a decrease of ~20% in the hot-spot flux in 2008-2009, to a stable, minimum value. However, the permanence of the high-amplitude, thermal X-ray pulse, even after the radio demise, implies continuing magnetar activity
Practical approaches to analyzing PTA data: Cosmic strings with six pulsars
We search for a stochastic gravitational wave background (SGWB) generated by
a network of cosmic strings using six millisecond pulsars from Data Release 2
(DR2) of the European Pulsar Timing Array (EPTA). We perform a Bayesian
analysis considering two models for the network of cosmic string loops, and
compare it to a simple power-law model which is expected from the population of
supermassive black hole binaries. Our main strong assumption is that the
previously reported common red noise process is a SGWB. We find that the
one-parameter cosmic string model is slightly favored over a power-law model
thanks to its simplicity. If we assume a two-component stochastic signal in the
data (supermassive black hole binary population and the signal from cosmic
strings), we get a upper limit on the string tension of () for the two cosmic string models we consider. In extended
two-parameter string models, we were unable to constrain the number of kinks.
We test two approximate and fast Bayesian data analysis methods against the
most rigorous analysis and find consistent results. These two fast and
efficient methods are applicable to all SGWBs, independent of their source, and
will be crucial for analysis of extended data sets.Comment: 13 pages, 5 figure
The second data release from the European Pulsar Timing Array I. The dataset and timing analysis
Pulsar timing arrays offer a probe of the low-frequency gravitational wave
spectrum (1 - 100 nanohertz), which is intimately connected to a number of
markers that can uniquely trace the formation and evolution of the Universe. We
present the dataset and the results of the timing analysis from the second data
release of the European Pulsar Timing Array (EPTA). The dataset contains
high-precision pulsar timing data from 25 millisecond pulsars collected with
the five largest radio telescopes in Europe, as well as the Large European
Array for Pulsars. The dataset forms the foundation for the search for
gravitational waves by the EPTA, presented in associated papers. We describe
the dataset and present the results of the frequentist and Bayesian pulsar
timing analysis for individual millisecond pulsars that have been observed over
the last ~25 years. We discuss the improvements to the individual pulsar
parameter estimates, as well as new measurements of the physical properties of
these pulsars and their companions. This data release extends the dataset from
EPTA Data Release 1 up to the beginning of 2021, with individual pulsar
datasets with timespans ranging from 14 to 25 years. These lead to improved
constraints on annual parallaxes, secular variation of the orbital period, and
Shapiro delay for a number of sources. Based on these results, we derived
astrophysical parameters that include distances, transverse velocities, binary
pulsar masses, and annual orbital parallaxes.Comment: 29 pages, 9 figures, 13 tables, Astronomy & Astrophysics in pres
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